Studies in this laboratory are designed to elucidate the role of DNA repair processes in human diseases and in carcinogenesis and in normal and abnormal aging. Most studies have been conducted with cells from patients with xeroderma pigmentosum (XP) who have defective DNA repair plus multiple cutaneous malignancies, premature aging of sun-exposed skin and the nervous system. Studies are currently being performed on cells from patients with degenerative neurological diseases such as Huntington's disease, ataxia telangiectasia, familial dysautonomia, olivopontocerebellar atrophy, spinal muscular atrophy, muscular dystrophy, and retinitis pigmentosa. These studies are designed to elucidate the pathogenesis of these disorders as well as to develop presymptomatic diagnostic tests. We assess the biological effectiveness of DNA repair primarily by in vitro assays of cell survival after treatment of the cells with DNA damaging agents.